Contamination ? of PPtF CCDs

[Derek Ives]

Hi CCD gurus,
	 I was wondering if anyone else out there was running the Passivated Platinum Film 
LORAL devices as produced by Mike and his group at Steward. I am having problems with the 
QE remaining stable with time and/or temperature. This may be due to some form of 
contamination ( of water vapour ? ) possibly in our dewars.  We use standard Oxford 
Instruments dewars, made from aluminum with mylar film taped to the inner surfaces , some 
stainless bits and pieces and not much else. We do use a small no. of 'O' rings with Fomblin very 
high vacuum grease.
We can bake the CCDs out in the dewars and this process "reactivates" the QE response of the 
CCDs. If we then leave the CCDs in the dewars under vacuum but at room temp.  for a few days 
and then repeat the QE measurements (in diode mode - its very quick) we find that it has 
dropped off significantly, especially in the blue. We also find that the QE in the blue reduces with 
temperature. 

				Regards,
					Derek Ives

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